Not only does Monero already do what ZCash is trying to do, but it has two main advantages:
1. EVERY transaction is private, which means that the entropy of the anonymityset is continuously growing. Instead, ZCash restricts privacy to an opt-in mechanism (mostly due to private transactions being horrible - requiring north of 8gb of RAM and several minutes on a modern computer) which means that there is a trivial amount of entropy, and deanonymization is pretty trivial.
2. Monero is focusing on further improvements that ZCash is just dreaming about, such as their C++ i2p router, Kovri. They can do this because they've been in production, tested, and hammered for several years.
The real question is: what does ZCash provide that Monero doesn't, except some sort of ridiculous "star cred"?
I agree with your other criticism of Zcash though. The situation is far from perfect.
So you can't claim Monero already solved all the problems that Zcash is trying to solve.